Phase diagram and upper critical field of homogenously disordered epitaxial 3-dimensional NbN films

TL;DR

This study explores how disorder affects superconductivity in 3D NbN films, revealing a quantum critical point where metal-insulator and superconductor-insulator transitions coincide.

Contribution

It presents a phase diagram for disordered NbN films and demonstrates the simultaneous occurrence of metal-insulator and superconductor-insulator transitions at a quantum critical point.

Findings

Superconducting transition temperature decreases with increasing disorder.

Metal-insulator transition coincides with superconductor-insulator transition at kFl~1.

Phase diagram maps the evolution of superconductivity with disorder.

Abstract

We report the evolution of superconducting properties with disorder, in 3-dimensional homogeneously disordered epitaxial NbN thin films. The effective disorder in NbN is controlled from moderately clean limit down to Anderson metal-insulator transition by changing the deposition conditions. We propose a phase diagram for NbN in temperature-disorder plane. With increasing disorder we observe that as kFl-->1 the superconducting transition temperature (Tc) and minimum conductivity (sigma_0) go to zero. The phase diagram shows that in homogeneously disordered 3-D NbN films, the metal-insulator transition and the superconductor-insulator transition occur at a single quantum critical point at kFl~1.